The following relates to the illumination arts, lighting arts, electrical power arts, and related arts.
Light emitting diode (LED)-based lamps are employed in diverse outdoor lighting and illumination systems, such as traffic lighting, overhead (e.g., post-mounted) lamps, billboard and other commercial illuminated signage, and so forth. These lighting or illumination systems are sometimes in the context of commercial or industrial applications, such as commercial signage, parking lot illumination for retail centers, malls, supermarkets, and the like, or so forth.
In commercial and industrial settings, the available electrical power is typically three-phase a.c. power, such as 120/208 V or 277/480 V three-phase power as is typical in commercial or industrial settings in the United States, or 220/380 V three phase power in China, or so forth. The three-phase power is typically high voltage (for example, over 100 volts per phase). For high operating efficiency, the powered load should be balanced amongst the three phases.
LED-based lamps, on the other hand, are typically driven by d.c. power, since the diodes have polarity and do not operate under “negative” bias. Light emitting diodes also typically operate at relatively low voltage (a few volts across the p/n junction) and at relatively high current (of order a few hundred milliamperes to a few amperes current flow through each diode). Thus, LED-based lamps are generally not well-matched to three-phase a.c. power.
In a known approach for driving an LED-based lamp using three-phase a.c. power, the lamp is driven by one phase of a Y-connected three-phase a.c. power source (i.e., between the phase and ground), or is driven across two phases of a Y- or Δ-connected a.c. power source. To balance the load, a plural number of such LED-based lamps are distributed in balanced fashion amongst the phases of the power source. The generally sinusoidal a.c. phase-to-ground or phase-to-phase voltage is converted to d.c. using a costly electrolytic capacitor as a filter. Still further, for efficient power usage a power factor (PF) correction circuit is employed to ensure the LED-based lamp is driven at a PF close to unity.
These approaches employ complex and costly circuitry. Additionally, these are nonstandard approaches for drawing power off the three-phase a.c. distribution bus. As a result, the electrical connection of an LED-based lamp typically requires performing substantial electrical work at the three-phase a.c. power distribution panel, such as installing one or more dedicated phase-to-ground or phase-to-phase power taps. Such extensive electrical work at the distribution panel is undesirable and can introduce substantial safety concerns.
Another consideration is the location of the power conversion system. In commercial or industrial settings, LED-based lamps are sometimes mounted in locations that are remote or difficult to access. Examples include post-mounted lamps, illuminated channel letter signage mounted on an elevated billboard or building wall, or so forth. Typically, underground conduits supply the a.c. power at ground level. In one approach, the power conversion circuitry is mounted proximate to the elevated lamp. This approach adversely impacts maintenance. If the power circuitry fails or needs repair, a crew of typically three persons (an electrician, an lift operator, and a third “safety spotter”) are required to perform the maintenance at the location of the elevated lamp. In another approach, the power conversion circuitry is located at ground level. However, this approach has the disadvantage of requiring low voltage, high current d.c. electrical power to be conducted from ground level to the elevated location of the lamp, which increases “I2R” resistive power losses. Additionally, this approach may entail adding a dedicated weatherproof housing at ground level to house the specialized power conversion circuitry for the LED-based lamp.